1. Field of the Invention
The present invention relates generally to systems for controlling the operation of motors and, more particularly, to a system for simultaneously and independently controlling a plurality of electric motors from a number of dispersed stations without interaction.
2. The Prior Art
In the operation of model railroads, a need exists to control a number of model railroad locomotives running on a common track. The control for each of the locomotives is to be reliable, simultaneous and independent as between locomotives. One such known system powers the common track by a low voltage 60 Hz AC power. Each locomotive motor is controlled by a receiver tuned to a particular frequency which modulates the low voltage 60 Hz AC propulsion power. Forward motor rotation is effected by detecting the modulation on one half cycle of the low voltage 60 Hz AC power and reverse motor rotation is effected by detecting the modulation on the other half cycle. Full speed for the motors can, of course, only be had from the respective one half wave rectified 60 Hz AC power. In addition to the resultant noisy operation, this system incorporates a flaw in that if the applied low voltage 60 Hz AC power is phase shifted 180.degree., then all motors on the track powered from that 60 Hz AC will start running in reverse. Also, due to the use of AC power for propulsion, the control signals are easily shorted or swamped by resistive loading, such as by light bulbs in cars or locomotives.
Another known system employs low voltage DC power to power the common track and the receivers and to provide the propulsion power to the locomotive motors. A pulse train is used to modulate the low voltage DC power. The spacing between successive pulses, i.e., pulse position modulation, represents the control to a specific motor. The system uses circuitry that is complex, somewhat cumbersome, hence expensive.